Eighty cars were destroyed or badly damaged in a devastating fire at Sydney's Olympic Park which investigators on Monday said was likely started by a "stupid" individual discarding a cigarette.

Eighty cars were destroyed or badly damaged in a devastating fire at Sydney's Olympic Park which investigators on Monday said was likely started by a "stupid" individual discarding a cigarette.

More than 50 firefighters battled the blaze in the car park at the Sydney Aquatic Centre, scene of the 2000 Olympics, during heatwave conditions on Sunday with hundreds of people evacuated as petrol tanks exploded and tyres blew.

A line of 47 burned-out cars and 33 others badly damaged greeted onlookers Monday, with New South Wales Fire Commissioner Greg Mullins saying a cigarette butt probably caused a grass fire with strong winds quickly spreading it to the vehicles.

"In all my years fighting fires -- 42 years -- I've never seen a fire move through cars like that. The fire was leaping from car to car, being driven by the wind. It was quite amazing," he said.

He described the conditions as "quite horrendous" with soaring temperatures and gusting, dry winds and said whoever threw the butt was "stupid".

"That's all it took, and I have to say that people just don't heed the warnings. On days like that you just can't afford to throw away a cigarette butt, it's irresponsible, stupid."

No-one was injured.

Firefighters on Sunday had to battle temperatures that jumped to 36 Celsius coupled with high winds that also fanned a series of blazes at Port Stephens, 160 kilometres (99 miles) north of Sydney which destroyed five houses at the popular holiday destination.

Cooler conditions on Monday were helping their battle to contain those fires.